Class ReferenceSensitiveOptional

tests/test_stl.cpp:124–162

// See issue #3330 for more details.
template <typename T>
class ReferenceSensitiveOptional {
public:
    using value_type = T;

    ReferenceSensitiveOptional() = default;
    // NOLINTNEXTLINE(google-explicit-constructor)
    ReferenceSensitiveOptional(const T &value) : storage{value} {}
    // NOLINTNEXTLINE(google-explicit-constructor)
    ReferenceSensitiveOptional(T &&value) : storage{std::move(value)} {}
    ReferenceSensitiveOptional &operator=(const T &value) {
        storage = {value};
        return *this;
    }
    ReferenceSensitiveOptional &operator=(T &&value) {
        storage = {std::move(value)};
        return *this;
    }

    template <typename... Args>
    T &emplace(Args &&...args) {
        storage.clear();
        storage.emplace_back(std::forward<Args>(args)...);
        return storage.back();
    }

    const T &value() const noexcept {
        assert(!storage.empty());
        return storage[0];
    }

    const T &operator*() const noexcept { return value(); }

    const T *operator->() const noexcept { return &value(); }

    explicit operator bool() const noexcept { return !storage.empty(); }

private:
    std::vector<T> storage;
};

namespace PYBIND11_NAMESPACE {
namespace detail {